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The largest study to date has confirmed that elderly patients who take certain high-potency cholesterol-lowering drugs known as statins have an increased risk of developing diabetes relative to a lower-potency statin, pravastatin.

However, no significantly increased risk was evident with two other statins relative to pravastatin, according to the paper published today on bmj.com.

“Our findings are significant because statins are among the most commonly used drugs in the world and our findings suggest that certain statins may confer a slightly increased risk of diabetes relative to other statins among those without a history of diabetes,” said Dr. Muhammad Mamdani, a scientist at the Li Ka Shing Knowledge Institute of St. Michael’s Hospital and senior author of the study.

Statins are prescribed not just for lowering cholesterol to prevent cardiovascular events but also for people who have already had cardiovascular incidents such as a heart attack, stroke or peripheral artery disease. They are considered to be highly effective, but recent research has linked them to an increased risk of developing Type 2 diabetes, commonly known as adult onset diabetes.

In January, Health Canada required new labelling for statins to point out these risks, which it said were found mainly in patients with pre-existing risk factors for diabetes such as high levels of glucose in the blood, being obese or having high blood pressure.

Dr. Muhammad, an adjunct scientist with the Institute for Clinical Evaluative Sciences, used the health records of 1.5 million residents in Ontario to examine the association between statin use and new-onset diabetes.The patients were aged 66 and over and started statin therapy between 1997 and 2010. Atorvastatin accounted for more than half of all new statin prescriptions followed by rosuvastatin, simvastatin, pravastatin, lovastatin and fluvastatin. The study used pravastatin-treated patients as the comparison group as pravastatin has been shown to have favourable effects on diabetes in animals and in clinical trials.

This was the largest study to date to directly compare individual statins with respect to a risk for diabetes. The study demonstrated significant increased risk of diabetes with some statins relative to others among irrespective of whether the patient had a prior history of cardiovascular events.

Of the 471,250 patients they identified with no history of diabetes and who were newly treated with a statin, patients treated with atorvastatin were found to have a 22 percent increased relative risk of new-onset diabetes compared to patients treated with pravastatin.

Rosuvastatin was linked to an 18 percent relative increased risk and simvastatin a 10 percent relative increased risk, relative to pravastatin. In contrast, patients treated with fluvastatin and lovastatin did not demonstrate an increased risk.

The researchers say several factors may explain the increased risk of developing diabetes, including the possibility that certain statins could block the release of insulin, the hormone that manages blood sugar levels.

“Overall, the risk of developing diabetes among patients taking statins appears to be low and may not outweigh the benefits of statin therapy in moderate to high risk patients,” said Dr. Mamdani. “For example, for every 1,000 persons treated with atorvastatin, only about six to eight additional people will be diagnosed with diabetes relative to those taking pravastatin. Both pravastatin and atorvastatin can be used for most patients to prevent future cardiovascular events, however our findings suggest pravastatin may confer a slightly lower risk of incident diabetes. ”

Dr. Mamdani, a PharmD, is the director of the Applied Health Research Centre at St. Michael’s. The AHRC is an academic research centre that specializes in designing and conducting clinical research, including multi-centre clinical trials. It offers start-to-finish assistance to researchers who have an idea for a clinical trial but lack the experience or infrastructure to conduct one – from designing high-quality studies to operationalizing a study and drawing up a budget to providing secure informatics services and data management storage in more than 20 different languages, crunching the numbers and analyzing the results with highly trained statisticians.

AHRC recently joined with two other St. Michael’s groups to form a clinical research services group known as HUB Health Research Solutions. The other two groups are BreaKThrough Knowledge Translation Services, led by Dr. Sharon Straus, and the Centre for ExceLlence in Economic Analysis Research (CLEAR), led by Dr. Jeffrey Hoch.

This study was funded by the Drug Innovation Fund of the Ontario Ministry of Health and Long-Term Care.

About St. Michael’s Hospital

St Michael’s Hospital provides compassionate care to all who enter its doors. The hospital also provides outstanding medical education to future health care professionals in more than 23 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, care of the homeless and global health are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing International Healthcare Education Centre, which make up the Li Ka Shing Knowledge Institute, research and education at St. Michael’s Hospital are recognized and make an impact around the world. Founded in 1892, the hospital is fully affiliated with the University of Toronto.